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Thanks. The reply from Stefan Kottwitz is helpful in pointing to the reason for my problems, because I did in fact try kpsewhich but got null response.
However, my system's response to
which kpsewhich is /usr/local/texlive/2014/bin/universal-darwin/kpsewhich .
Since the file I was searching for is ...

I have just joined Latex Community, and I am not familiar with it, so I hope I haven't missed the answer to my questions below.
I have searched but I have not been able to find answers.

I have just installed MacTeX. I'm using command line
latexmk -pdf filename.tex
to compile. The first line of my ...